The present invention is relevant for the field of data bases, especially data base systems handling huge numbers of data. In this connection the patent applications WO 02/061612 A2 and WO 02/061613 A2 disclose—amongst others—such data base systems, data structures used therein and query optimizers for such data base systems. The disclosure of both these applications is incorporated herein by reference. These applications especially reflect storage and query strategies based on balanced binary trees.
Furtheron reference is made to European patent application 03 015 365.4 (prior art according to article 54(3) EPC), which basically discloses the method of storing certain query results as bitmaps, which is a very simple and machine-oriented strategy of storing data. Again the contents of this older patent application is incorporated herein by reference.
In case the result of a query exists as a bitmap—the so-called result bitmap—the bits with value 1 in this result bitmap represent datasets in which the query condition is given. Now if a user of a data base system wants to know the number of hits of a query the usual strategy is to count the bits set to value 1 in the result bitmap and to thus determine the number of relevant datasets. Such exact count is performed by scanning through the bitmap data structure machine word by machine word, determine the set bits and add a value 1 to an according counter in case a set bit was determined. At the end of this process the counter variable contains the exact number of hits.